In recent years, augmented reality technology (AR technology: Augmented Reality) in which a virtual object or various kinds of information serving as supplementary information is combined with a real environment (or a part thereof) and then presented as electronic information has been focused on. In order to realize the augmented reality technology, for example, a head mounted display has been considered as a device for presenting visual information. In addition, as fields of its application, work support in real environments including, for example, provision of road guidance information, provision of technical information to technicians who perform maintenance, and the like is expected to be provided. Particularly, such a head mounted type display is very convenient because the display can be used without hands. In addition, even when one wishes to view a video or an image while moving outside, the video or the image and an external environment can be simultaneously perceived in a visual field, and thus free movement is possible.
A virtual image display device (image display device) for allowing an observer to observe a two-dimensional image formed by an image forming device as a virtual image enlarged by a virtual image optical system is well known, for example, from JP 2006-162767A.
As illustrated in the conceptual diagram of FIG. 47, an image display device 100′ includes an image forming device 111 having a plurality of pixels arranged in a 2D matrix, a collimating optical system 112 which collimates light output from a pixel of the image forming device 111 into parallel light, and an optical device (light guide unit) 120 on which light that has turn into the parallel light from the collimating optical system 112 is incident, through which the light is guided, and from which the light is output. The optical device 120 includes a light guide plate 121 which outputs the incident light after the incident light propagates through the inside according to total reflection, a first deflecting unit 130 (for example, including a light reflecting film of one layer) which reflects the light incident on the light guide plate 121 so that the light incident on the light guide plate 121 is totally reflected inside the light guide plate 121, and a second deflecting unit 140 (for example, including a light reflecting multi-film having a multi-layer laminated structure) which outputs from the light guide plate 121 the light propagating through the inside of the light guide plate 121 according to the total reflection. A weight and size of a device can be reduced, for example, when the HMD is formed according to such an image display device 100′. With regard to reference numerals denoting other constituent elements in FIG. 47, an image display device of Embodiment 1 that will be described with reference to FIG. 1 will be referred to.
Alternatively, in order to allow an observer to observe a 2D image formed by the image forming device as a virtual image enlarged by the virtual image optical system, a virtual image display device (image display device) using hologram diffraction gratings is well known, for example, from JP 2007-94175A.
As illustrated in the conceptual diagram of FIG. 48, an image display device 300′ basically includes an image forming device 111 which displays an image, a collimating optical system 112, and an optical device (a light guide unit) 320 on which light displayed on the image forming device 111 is incident and through which the incident light is guided to a pupil 21 of the observer. Here, the optical device 320 includes a light guide plate 321 and a first diffraction grating member 330 and a second diffraction grating member 340 formed by reflective volume hologram diffraction gratings provided on the light guide plate 321. Light output from each pixel of the image forming device 111 is incident on the collimating optical system 112, and a plurality of parallel light beams having different angles incident on the light guide plate 321 is generated by the collimating optical system 112 and incident on the light guide plate 321. The parallel light is incident on and output from a first surface 322 of the light guide plate 321. On the other hand, the first diffraction grating member 330 and the second diffraction grating member 340 are mounted on a second surface 323 of the light guide plate 321 parallel to the first surface 322 of the light guide plate 321. With regard to reference numerals denoting other constituent elements in FIG. 48, an image display device of Embodiment 7 that will be described with reference to FIG. 11 will be referred to.
In addition, by displaying images on the image display device 100′ or 300′, the observer can view the displayed images superimposed on images of the outer field.
However, due to extreme brightness of the environment around the position in which the image display device 100′ or 300′ is placed or the content of an image being displayed, a problem that sufficient contrast is not given to an image to be observed by an observer can occur. Thus, a measure for solving this problem is known from, for example, JP 2004-101197A. In the technology disclosed in the patent publication, an incidence amount of external light is controlled by a liquid crystal shutter.